Lubricating oils for use in crankcase engine oils contain components which are used to improve the viscometric performance of the engine oil, i.e., to provide for multigrade engine oils, such as SAE 5W-30, 10W-30, and 10W-40, etc. These viscosity performance enhancers, commonly referred to as viscosity index (VI) improvers, include olefin copolymers, polymethacrylates, and styrene/hydrogenated diene block and star copolymers. These materials are often called nondispersant VI improvers because they do not help prevent varnish or sludge in the oil from depositing on the inside of an internal combustion engine.
To prevent this sludge from depositing on the engine parts, dispersants, commonly referred to as ashless dispersants, are added to the motor oil. These dispersants keep the sludge and varnish materials suspended in the oil and prevent them from forming deposits in the engine. The current industry standard test for engine cleanliness is the ASTM Sequence VE test (measuring sludge, varnish, and wear in the engine). For an ashless dispersant to be considered effective, it must allow a motor oil formulated with a nondispersant VI improver to pass this test while passing the industry standard ASTM Sequence VIA fuel economy test as well as other tests required by the industry. Generally, the fuel economy suffers as more ashless dispersant is added to the motor oil. A dispersant VI improver can replace ashless dispersant and still maintain good engine cleanliness in the Sequence VE test. In addition, it will give better fuel economy in the Sequence VIA fuel economy test.
It is therefore an objective of this invention to provide a lubricating oil dispersant viscosity index improver which is highly effective and able to replace a substantial amount of the ashless dispersant additive normally used in an engine oil. This invention describes such a dispersant VI improver and a process for its preparation.
For instance, a typical crankcase engine oil composition contains from about 80 to 95 percent by weight of base oil, 0.1 to 3 a percent of a viscosity index improver (VII), and from 5 to 20 percent of a dispersant inhibitor (DI) package which contains an ashless dispersant. The viscosity index improver described herein is a non-dispersant VII. This is the reason that the ashless dispersant is required in this composition. The active components of the DI package normally contains about 50 to 60 percent by weight (% wt) of the ashless dispersant, the balance being comprised of other ingredients such as a detergent, an anti-wear agent, an antioxidant and various other minor additives. The oil compositions using the dispersant viscosity index improvers (DVII) of the present invention will still contain about 80 to 95 percent of the base oil and from 0.1 to 3 percent of the dispersant viscosity index improver which may be entirely made up of the novel DVII of the present invention or may be a mix of said DVII with a non-dispersant viscosity index improver.
The DI package will still comprise from about 5 to 20 percent by weight of the crankcase oil composition. However, it will be shown below that equivalent performance to the performance of the prior art typical oil composition can be achieved with the oil composition of the present invention wherein the DI package contains from 0 to 60 percent of the amount of ashless dispersant used in the DI package of the prior art typical oil composition. Thus, the present invention allows the amount of ashless dispersant to be reduced by at least 40 percent compared to the amount needed with a non-dispersant viscosity index improver, i.e., the typical oil composition described above.